Leetcode102: Search in Rotated Sorted Array

Suppose a sorted array is rotated at some pivot unknown to you beforehand.

(i.e.,

0 1 2 4 5 6 7

might become

4
5 6 7 0 1 2

).

You are given a target value to search. If found in the array return its index, otherwise return -1.

You may assume no duplicate exists in the array.

如果中间元素大于首部元素，那么表明查找区间左半部分是有序的，然后再根据target是否在有序的一部分来决定接下来查找的方向

如果中间元素小于首部元素，那么查找区间有半部分是有序的，然后再根据target是否在有序的一部分来决定接下来查找的方向

class Solution {
public:
int search(vector<int>& nums, int target) {
int n = nums.size();
if(n==0)    return -1;
int l = 0;
int r = n-1;
while(l<=r)
{
int mid = (l+r)/2;
if(nums[mid] == target) return mid;
if(nums[l] <= nums[mid])
{
if(nums[l]<=target && target<nums[mid])
r = mid-1;
else
l = mid+1;
}
else
{
if(nums[mid]<target && target<=nums[r])
l = mid+1;
else
r = mid-1;
}
}
return -1;
}
};